Secretory interleukin-1 receptor antagonist gene expression requires both a PU.1 and a novel composite NF-kappaB/PU.1/ GA-binding protein binding site

Variants at the Interleukin 1 Gene Locus and Pericarditis

Importance

Recurrent pericarditis is a treatment challenge and often a debilitating condition. Drugs inhibiting interleukin 1 cytokines are a promising new treatment option, but their use is based on scarce biological evidence and clinical trials of modest sizes, and the contributions of innate and adaptive immune processes to the pathophysiology are incompletely understood.

Objective

To use human genomics, transcriptomics, and proteomics to shed light on the pathogenesis of pericarditis.

Design, Setting, and Participants

This was a meta-analysis of genome-wide association studies of pericarditis from 5 countries. Associations were examined between the pericarditis-associated variants and pericarditis subtypes (including recurrent pericarditis) and secondary phenotypes. To explore mechanisms, associations with messenger RNA expression (cis-eQTL), plasma protein levels (pQTL), and CpG methylation of DNA (ASM-QTL) were assessed. Data from Iceland (deCODE genetics, 1983-2020), Denmark (Copenhagen Hospital Biobank/Danish Blood Donor Study, 1977-2022), the UK (UK Biobank, 1953-2021), the US (Intermountain, 1996-2022), and Finland (FinnGen, 1970-2022) were included. Data were analyzed from September 2022 to August 2023.

Exposure

Genotype.

Main Outcomes and Measures

Pericarditis.

Results

In this genome-wide association study of 4894 individuals with pericarditis (mean [SD] age at diagnosis, 51.4 [17.9] years, 2734 [67.6%] male, excluding the FinnGen cohort), associations were identified with 2 independent common intergenic variants at the interleukin 1 locus on chromosome 2q14. The lead variant was rs12992780 (T) (effect allele frequency [EAF], 31%-40%; odds ratio [OR], 0.83; 95% CI, 0.79-0.87; P = 6.67 × 10-16), downstream of IL1B and the secondary variant rs7575402 (A or T) (EAF, 45%-55%; adjusted OR, 0.89; 95% CI, 0.85-0.93; adjusted P = 9.6 × 10-8). The lead variant rs12992780 had a smaller odds ratio for recurrent pericarditis (0.76) than the acute form (0.86) (P for heterogeneity = .03) and rs7575402 was associated with CpG methylation overlapping binding sites of 4 transcription factors known to regulate interleukin 1 production: PU.1 (encoded by SPI1), STAT1, STAT3, and CCAAT/enhancer-binding protein β (encoded by CEBPB).

Conclusions and Relevance

This study found an association between pericarditis and 2 independent sequence variants at the interleukin 1 gene locus. This finding has the potential to contribute to development of more targeted and personalized therapy of pericarditis with interleukin 1-blocking drugs.

Activation of Toll-Like Receptor 3 Induces Interleukin-1 Receptor Antagonist Expression by Activating the Interferon Regulatory Factor 3

Toll-like receptor 3 (TLR3) is a sensor of endogenous cell necrosis during the process of acute inflammation. Interleukin (IL)-1 receptor antagonist (IL-1Ra) is an anti-inflammatory cytokine and can negatively regulate the pathogenesis of inflammation. However, whether and how activation of TLR3 can regulate IL-1Ra expression has not been clarified. Here, we show that poly(I:C) induces IL-1Ra expression in primarily cultured human fibroblast-like synoviocytes and other types of cells. Induction of IL-1Ra by poly(I:C) was dependent on TLR3, but was independent of melanoma differentiation--associated protein 5 or retinoic acid-inducible gene I. Interferon regulatory factor 3 (IRF3) directly binds to the IL-1Ra promoter and promotes IL-1Ra expression in response to poly(I:C) stimulation. Induction of IL-1Ra by poly(I:C) was abolished by the inhibition of the NF-κB signaling, attenuated by the inhibition of the PI3K-Akt signaling, enhanced by inhibition of the ERK1/2 or MSK1/2 activation, but was independent of the p38 MAPK signaling. Treatment with poly(I:C) or Sendai virus elevated the levels of serum IL-1Ra in wild-type, but not in TLR3-/- or IRF3-/- mice. Our findings may provide new insights into the intrinsic anti-inflammatory function of TLR3 and double-stranded RNA-induced IL-Ra expression by TLR3 and its regulation.

Latent viruses can cause disease by disrupting the competition for the limiting factor p300/CBP

CBP and p300 are histone acetyltransferase coactivators that control the transcription of numerous genes in humans, viruses, and other organisms. Although two separate genes encode CBP and p300, they share a 61% sequence identity, and they are often mentioned together as p300/CBP. Zhou et al. showed that under hypoxic conditions, HIF1α and the tumor suppressor p53 compete for binding to the limiting p300/CBP coactivator. Jethanandani & Kramer showed that δEF1 and MYOD genes compete for the limited amount of p300/CBP in the cell. Bhattacharyya et al. showed that the limiting availability of p300/CBP in the cell serves as a checkpoint for HIF1α activity. Here, we use the microcompetition model to explain how latent viruses with a specific viral cis-regulatory element in their promoter/enhancer can disrupt this competition, causing diseases such as cancer, diabetes, atherosclerosis, and obesity.

Differential sensitivity to methylated DNA by ETS-family transcription factors is intrinsically encoded in their DNA-binding domains

Transactivation by the ETS family of transcription factors, whose members share structurally conserved DNA-binding domains, is variably sensitive to methylation of their target genes. The mechanism by which DNA methylation controls ETS proteins remains poorly understood. Uncertainly also pervades the effects of hemi-methylated DNA, which occurs following DNA replication and in response to hypomethylating agents, on site recognition by ETS proteins. To address these questions, we measured the affinities of two sequence-divergent ETS homologs, PU.1 and Ets-1, to DNA sites harboring a hemi- and fully methylated CpG dinucleotide. While the two proteins bound unmethylated DNA with indistinguishable affinity, their affinities to methylated DNA are markedly heterogeneous and exhibit major energetic coupling between the two CpG methylcytosines. Analysis of simulated DNA and existing co-crystal structures revealed that hemi-methylation induced non-local backbone and groove geometries that were not conserved in the fully methylated state. Indirect readout of these perturbations was differentially achieved by the two ETS homologs, with the distinctive interfacial hydration in PU.1/DNA binding moderating the inhibitory effects of DNA methylation on binding. This data established a biophysical basis for the pioneering properties associated with PU.1, which robustly bound fully methylated DNA, but not Ets-1, which was substantially inhibited.

Deficiency of C-C chemokine receptor 5 suppresses tumor development via inactivation of NF-κB and upregulation of IL-1Ra in melanoma model

To evaluate the relevance of C-C chemokine receptor type 5 (CCR5) expression and tumor development, we compared melanoma growth in CCR5 knockout (CCR5^−/−) mice and wild type (CCR5^+/+) mice. CCR5^−/− mice showed reduced tumor volume, tumor weight, and increased survival rate when compared to CCR5^+/+ mice. We investigated the activation of NF-κB since it is an implicated transcription factor in the regulation of genes involving cell growth, apoptosis, and tumor growth. Significant inhibition of DNA binding activity of NF-κB, and translocation of p50 and p65 into the nucleus through the inhibition of phosphorylation of IκB was found in the melanoma tissues of CCR5^−/− mice compared to melanoma tissues of CCR5^+/+ mice. NF-κB target apoptotic protein expression, such as cleaved caspase-3, cleaved PARP, and Bax, was elevated, whereas the survival protein expression levels, such as Bcl-2, C-IAP1, was decreased in the melanoma tissues of CCR5^−/− mice. Interestingly, we found that the level of IL-1Ra, a tumor growth suppressive cytokine, was significantly elevated in tumor tissue and spleen of CCR5^−/− mice compared to the level in CCR5^+/+ mice. Moreover, infiltration of CD8⁺ cytotoxic T cell and CD57⁺ natural killer cells was significantly increased in melanoma tumor and spleen tissue of CCR5^−/− mice compared to that of CCR5^+/+ mice. Therefore, these results showed that CCR5 deficiency caused apoptotic cell death of melanoma through inhibition of NF-κB and upregulation of IL-1Ra.

Distinct peripheral blood RNA responses to Salmonella in pigs differing in Salmonella shedding levels: intersection of IFNG, TLR and miRNA pathways

Transcriptomic analysis of the response to bacterial pathogens has been reported for several species, yet few studies have investigated the transcriptional differences in whole blood in subjects that differ in their disease response phenotypes. Salmonella species infect many vertebrate species, and pigs colonized with Salmonella enterica serovar Typhimurium (ST) are usually asymptomatic, making detection of these Salmonella-carrier pigs difficult. The variable fecal shedding of Salmonella is an important cause of foodborne illness and zoonotic disease. To investigate gene pathways and biomarkers associated with the variance in Salmonella shedding following experimental inoculation, we initiated the first analysis of the whole blood transcriptional response induced by Salmonella. A population of pigs (n = 40) was inoculated with ST and peripheral blood and fecal Salmonella counts were collected between 2 and 20 days post-inoculation (dpi). Two groups of pigs with either low shedding (LS) or persistent shedding (PS) phenotypes were identified. Global transcriptional changes in response to ST inoculation were identified by Affymetrix Genechip® analysis of peripheral blood RNA at day 0 and 2 dpi. ST inoculation triggered substantial gene expression changes in the pigs and there was differential expression of many genes between LS and PS pigs. Analysis of the differential profiles of gene expression within and between PS and LS phenotypic classes identified distinct regulatory pathways mediated by IFN-γ, TNF, NF-κB, or one of several miRNAs. We confirmed the activation of two regulatory factors, SPI1 and CEBPB, and demonstrated that expression of miR-155 was decreased specifically in the PS animals. These data provide insight into specific pathways associated with extremes in Salmonella fecal shedding that can be targeted for further exploration on why some animals develop a carrier state. This knowledge can also be used to develop rational manipulations of genetics, pharmaceuticals, nutrition or husbandry methods to decrease Salmonella colonization, shedding and spread.

PU.1 is a major transcriptional activator of the tumour suppressor gene LIMD1

LIMD1 is a tumour suppressor gene (TSG) down regulated in ∼80% of lung cancers with loss also demonstrated in breast and head and neck squamous cell carcinomas. LIMD1 is also a candidate TSG in childhood acute lymphoblastic leukaemia. Mechanistically, LIMD1 interacts with pRB, repressing E2F-driven transcription as well as being a critical component of microRNA-mediated gene silencing. In this study we show a CpG island within the LIMD1 promoter contains a conserved binding motif for the transcription factor PU.1. Mutation of the PU.1 consensus reduced promoter driven transcription by 90%. ChIP and EMSA analysis demonstrated that PU.1 specifically binds to the LIMD1 promoter. siRNA depletion of PU.1 significantly reduced endogenous LIMD1 expression, demonstrating that PU.1 is a major transcriptional activator of LIMD1.

NF-kappaB down-regulates expression of the B-lymphoma marker CD10 through a miR-155/PU.1 pathway

Cell-surface protein CD10 is a prognostic marker for diffuse large B-cell lymphoma (DLBCL), where high expression of CD10 is found in the germinal center B-cell (GCB) subtype and CD10 expression is low or absent in the activated B-cell (ABC) subtype. As compared with the GCB subtype, patients with ABC DLBCL have a poorer prognosis after standard treatment, and ABC tumor cells have higher NF-κB activity. Herein, we show that increased expression of the NF-κB target micro-RNA miR-155 is correlated with reduced expression of transcription factor PU.1 and CD10 in several B-lymphoma cell lines. Moreover, electromobility shift assays and luciferase reporter assays indicate that PU.1 can directly activate expression from the CD10 promoter. Expression of a DLBCL-derived mutant of the adaptor CARD11 (a constitutive activator of NF-κB) in the GCB-like human BJAB cell line or v-Rel in the chicken DT40 B-lymphoma cell line causes reduced expression of PU.1. The CARD11 mutant also causes a decrease in CD10 levels in BJAB cells. Similarly, overexpression of miR-155, which is known to down-regulate PU.1, leads to reduced expression of CD10 in BJAB cells. Finally, we show that CD10 expression is reduced in BJAB cells after treatment with the NF-κB inducer lipopolysaccharide (LPS). Additionally, miR-155 is induced by LPS treatment or expression of the CARD11 mutant in BJAB cells. These results point to an NF-κB-dependent mechanism for down-regulation of CD10 in B-cell lymphoma: namely, that increased NF-κB activity leads to increased miR-155, which results in decreased PU.1, and consequently reduced CD10 mRNA and protein.

MSK1 regulates the transcription of IL-1ra in response to TLR activation in macrophages

The activity of the pro-inflammatory cytokine IL (interleukin)-1 is closely regulated in vivo via a variety of mechanisms, including both the control of IL-1 production and secretion as well as naturally occurring inhibitors of IL-1 function, such as IL-1ra (IL-1 receptor antagonist). IL-1ra is homologous with IL-1, and is able to bind but not activate the IL-1 receptor. IL-1ra can be produced by a variety of cell types, and its production is stimulated by inflammatory signals. In the present study, we show that in macrophages the TLR (Toll-like receptor)-mediated induction of IL-1ra from both its proximal and distal promoters involves the p38 and ERK1/2 (extracellular-signal-regulated kinase 1/2) MAPK (mitogen-activated protein kinase) cascades. In addition, we show that MSK1 and 2 (mitogen- and stress-activated kinase 1 and 2), kinases activated by either ERK1/2 or p38 in vivo, are required for the induction of both IL-1ra mRNA and protein. MSKs regulate IL-1ra transcription via both IL-10-dependent and -independent mechanisms in cells. Consistent with this, knockout of MSK in mice was found to result in a decrease in IL-1ra production following LPS (lipopolysaccharide) injection. MSKs therefore act as important negative regulators of inflammation following TLR activation.

TLR4-independent and PKR-dependent interleukin 1 receptor antagonist expression upon LPS stimulation

Dendritic cells (DCs) induce innate immune responses by recognizing bacterial LPS through TLR4 receptor complexes. In this study, we compared gene expression profiles of TLR4 knockout (TLR4(neg)) DCs and wild type (TLR4(pos)) DCs after stimulating with LPS. We found that the expression of various inflammatory genes by LPS were TLR4-independent. Among them, interleukin 1 receptor antagonist (IL-1rn) was of particular interest since IL-1rn is a potent natural inhibitor of proinflammatory IL-1. Using RT-PCR, real-time PCR, immunoblotting and ELISA, we demonstrated that IL-1rn was induced by DCs stimulated with LPS in the absence of TLR4. 2-Aminopurine, a pharmacological PKR inhibitor, completely abrogated LPS-induced expression of IL-1rn in TLR4(neg) DCs, suggesting that LPS-induced TLR4-independent expression of IL-1rn might be mediated by PKR pathways. Considering that IL-1rn is a physiological inhibitor of IL-1, TLR4-independent and PKR-dependent pathways might be crucial in counter-balancing proinflammatory effector functions of DCs resulted from TLR4-dependent activation by LPS.

B cells from periodontal disease patients express surface Toll-like receptor 4

Chronic systemic inflammation links periodontal disease (PD) to increased incidence of cardiovascular disease. Activation of TLRs, particularly TLR4, promotes chronic inflammation in PD by stimulating myeloid cells. B cells from healthy individuals are generally refractory to TLR4 agonists as a result of low surface TLR4 expression. Unexpectedly, a significantly increased percentage of gingival and peripheral blood B cells from patients with PD expressed surface TLR4. Surface expression correlated with an active TLR4 promoter that mimicked the TLR4 promoter in neutrophils. B cells from PD patients were surface myeloid differentiation protein 2-positive and also packaged the enhancer of a proinflammatory cytokine, IL-1 beta, into an active structure, demonstrating that these cells harbor key characteristics of proinflammatory cell types. Furthermore, B cells lacked activating signatures of a natural IL-1 beta inhibitor, IL-1 receptor antagonist. Surprisingly, despite multiple signatures of proinflammatory cells, freshly isolated B cells from PD patients had decreased expression of TLR pathway genes compared with B cells from healthy individuals. Decreases in inflammatory gene expression were even more dramatic in B cells stimulated with a TLR4 ligand from a periodontal pathogen, Porphyromonas gingivalis LPS 1690. In contrast, B cell TLR4 was not activated by the prototypic TLR4 ligand Escherichia coli LPS. These findings raise the unexpected possibility that TLR4 engagement modulates B cell activation in PD patients.

Dynamic protein associations define two phases of IL-1beta transcriptional activation

IL-1beta is a key proinflammatory cytokine with roles in multiple diseases. Monocytes package the IL-1beta promoter into a "poised architecture" characterized by a histone-free transcription start site and constitutive transcription factor associations. Upon LPS stimulation, multiple proteins inducibly associate with the IL-1beta gene. To understand how the complex combination of constitutive and inducible transcription factors activate the IL-1beta gene from a poised structure, we measured temporal changes in NF-kappaB and IFN regulatory factor (IRF) association with IL-1beta regulatory elements. Association of the p65 subunit of NF-kappaB peaks 30-60 min post-monocyte stimulation, and it shortly precedes IRF-4 recruitment to the IL-1beta enhancer and maximal mRNA production. In contrast, IRF-8/enhancer association decreases poststimulation. To test the importance of delayed IRF-4/enhancer association, we introduced a mutated PU.1 protein shown to prevent PU.1-mediated IRF-4 recruitment to the enhancer sequence. Mutated PU.1 initially increased IL-1beta mRNA followed by decreased mRNA levels 2-3 h poststimulation. Taken together, these data support a dynamic model of IL-1beta transcriptional activation in which a combination of IRF-8 and p65 drives the initial phase of IL-1beta transcription, while PU.1-mediated IRF-4 recruitment to the enhancer is important for the second phase. We further demonstrate that activation of both NF-kappaB and IRF-4 depends on CK2 kinase activity. Because IRF-4/enhancer association requires CK2 but not p65 activation, we conclude that CK2 triggers the IRF-4 and p65 pathways independently to serve as a master regulator of IL-1beta transcription.

No response of plasma substance P, but delayed increase of interleukin-1 receptor antagonist to acute psychosocial stress

Psychosocial stress has been shown to induce inflammatory reactions, followed by the release of immunosuppressive glucocorticoids. This may be mediated by catecholamines or other stress reactive substances such as neuropeptides or cytokines. We here set out to explore the effects of acute psychosocial stress on plasma levels of substance P (SP), a possible mediator of stress-induced inflammatory reactions, and interleukin-1 receptor antagonist (IL-1ra). Twelve healthy male subjects (mean age 27 yrs.) were subjected to the psychosocial stress test "Trier Social Stress Test" (TSST) and a resting control condition. Blood and saliva samples were taken before, as well as 1, 20, 45, and 90 min after TSST or rest, respectively. Salivary cortisol and plasma SP and IL-1ra were measured using immunoassays, salivary alpha-amylase (sAA) was measured by an enzyme kinetic method, and plasma epinephrine (E) and norepinephrine (NE) were measured by HPLC. The TSST induced immediate increases of E, NE, and sAA, and a delayed increase of free cortisol. Plasma IL-1ra showed an even further delayed peak at 90 min after stress. Plasma levels of SP did not respond to stress. No significant associations between changes of stress hormones and IL-1ra or SP were found. We conclude that substance P, epinephrine, and norepinephrine are probably not involved in mediating peripheral inflammation following psychosocial stress, at least with respect to IL-1ra. Further studies have to reveal the mechanisms involved in the stress-induced up regulation of IL-1ra.

Beta-(1-->3)-D-glucan modulates DNA binding of nuclear factors kappaB, AT and IL-6 leading to an anti-inflammatory shift of the IL-1beta/IL-1 receptor antagonist ratio

BACKGROUND

Beta-1-->3-D-glucans represent a pathogen-associated molecular pattern and are able to modify biological responses. Employing a comprehensive methodological approach, the aim of our in vitro study was to elucidate novel molecular and cellular mechanisms of human peripheral blood immune cells mediated by a fungal beta-1-->3-D-glucan, i.e. glucan phosphate, in the presence of lipopolysaccharide (LPS) or toxic shock syndrome toxin 1 (TSST-1).

RESULTS

Despite an activation of nuclear factor (NF) kappaB, NFinterleukin(IL)-6 and NFAT similar to LPS or TSST-1, we observed no significant production of IL-1beta, IL-6, tumor necrosis factor alpha or interferon gamma induced by glucan phosphate. Glucan phosphate-treated leukocytes induced a substantial amount of IL-8 (peak at 18 h: 5000 pg/ml), likely due to binding of NFkappaB to a consensus site in the IL-8 promoter. An increase in IL-1receptor antagonist (RA) production (peak at 24 h: 12000 pg/ml) by glucan phosphate-treated cells positively correlated with IL-8 levels. Glucan phosphate induced significant binding to a known NFIL-6 site and a new NFAT site within the IL-1RA promoter, which was confirmed by inhibition experiments. When applied in combination with either LPS or TSST-1 at the same time points, we detected that glucan phosphate elevated the LPS- and the TSST-1-induced DNA binding of NFkappaB, NFIL-6 and NFAT, leading to a synergistic increase of IL-1RA. Further, glucan phosphate modulated the TSST-1-induced inflammatory response via reduction of IL-1beta and IL-6. As a consequence, glucan phosphate shifted the TSST-1-induced IL-1beta/IL-1RA ratio towards an anti-inflammatory phenotype. Subsequently, glucan phosphate decreased the TSST-1-induced, IL-1-dependent production of IL-2.

CONCLUSION

Thus, beta-1-->3-D-glucans may induce beneficial effects in the presence of pro-inflammatory responses, downstream of receptor binding and signaling by switching a pro- to an anti-inflammatory IL-1RA-mediated reaction. Our results also offer new insights into the complex regulation of the IL-1RA gene, which can be modulated by a beta-1-->3-D-glucan.

Helicobacter pylori and toll-like receptor agonists induce syndecan-4 expression in an NF-kappaB-dependent manner

The syndecans are a family of transmembrane heparan sulfate proteoglycans (HSPG) that have been implicated in a wide variety of biological functions including the regulation of growth factor signaling, adhesion, tumorigenesis, and inflammation. In the current studies, we examined the regulation of syndecan-4 gene expression in gastric epithelial cells and macrophages in response to infection with live Helicobacter pylori and purified toll-like receptor (TLR) agonists. H. pylori, PAM3CSK4 (a TLR2 agonist), and Escherichia coli flagellin (a TLR5 agonist) all induced the rapid expression of syndecan-4 mRNA in MKN45 gastric epithelial cells. Similarly, lipopolysaccharide (LPS) (a TLR4 agonist) also induced the expression of syndecan-4 in macrophages. The H. pylori- and TLR-induced increase in syndecan-4 mRNA was blocked by the proteosome inhibitor MG-132 suggesting a role for nuclear factor kappaB (NF-kappaB) in the regulation of syndecan-4 gene expression. An 895-bp fragment of the human syndecan-4 promoter was cloned upstream of the luciferase reporter. When transfected into MKN45 cells, the activity of this promoter was inducible by H. pylori and TLR agonists. Inducible activity of the syndecan-4 promoter was blocked by cotransfection with a dominant negative IkappaBalpha expression plasmid. Electrophoretic mobility shift assays (EMSA) demonstrated the presence of a highly conserved NF-kappaB-binding site. Mutation of this site within the context of the full-length syndecan-4 promoter resulted in a complete loss of responsiveness to H. pylori and TLR agonists. These results thus demonstrate that the response of the syndecan-4 gene to infectious agents, or their products, is a direct result of NF-kappaB binding to the promoter and induction of de novo transcription.

Role of endogenous IL-10 in LPS-induced STAT3 activation and IL-1 receptor antagonist gene expression

The regulation of secretory interleukin (IL)-1 receptor antagonist (sIL-1Ra) in response to IL-10 is unique. In contrast to most cytokines, the lipopolysaccharide (LPS)-induced expression of the sIL-1Ra gene is enhanced by concomitant treatment with IL-10. Cotreatment of RAW 264.7 cells with IL-10 + LPS resulted in at least a twofold increase in sIL-1Ra promoter activity and mRNA expression compared with LPS alone; IL-10 alone had no effect on promoter activity or mRNA expression. Examination of sIL-1Ra mRNA expression in bone marrow-derived macrophages (BMDM) resulted in identical results. Transfection of RAW 264.7 cells with the sIL-1Ra/luc reporter and a dominant-negative signal transducer and activator of transcription (STAT)3 (Y705A) expression plasmid inhibited the enhanced response induced by exogenous IL-10 in the presence of LPS. The presence of a functional STAT3-binding site within the proximal sIL-1Ra promoter was demonstrated. As IL-10 is produced by LPS-stimulated macrophages, a role for endogenously produced IL-10 in the response of the sIL-1Ra gene to LPS was suggested. This was confirmed in IL-10-deficient BMDM, which when compared with normal BMDM, had significantly decreased LPS-induced sIL-1Ra mRNA levels that could be restored by exogenously provided IL-10, which induced a fivefold increase of LPS-induced IL-1Ra mRNA in cells from IL-10-/- BMDM. Western blot analysis of phosphorylated STAT3 from wild-type and IL-10-/- BMDM and IL-10 neutralization experiments demonstrated a role for endogenously produced IL-10 in the LPS-induced STAT3 activity. Together, these results demonstrate that endogenously produced IL-10 plays a significant role in LPS-induced sIL-1Ra gene expression via the activation of STAT3.

Identification and characterization of a PU.1/Spi-B binding site in the bovine leukemia virus long terminal repeat

Bovine leukemia virus (BLV) is a B-lymphotropic oncogenic retrovirus whose transcriptional promoter is located in the viral 5' long terminal repeat (LTR). To date, no B-lymphocyte-specific cis-regulatory element has been identified in this region. Since ETS proteins are known to regulate transcription of numerous retroviruses, we searched for the presence in the BLV promoter region of binding sites for PU.1/Spi-1, a B-cell- and macrophage-specific ETS family member. In this report, nucleotide sequence analysis of the viral LTR identified a PUbox located at -95/-84 bp. We demonstrated by gel shift and supershift assays that PU.1 and the related Ets transcription factor Spi-B interacted specifically with this PUbox. A 2-bp mutation (GGAA-->CCAA) within this motif abrogated PU.1/Spi-B binding. This mutation caused a marked decrease in LTR-driven basal gene expression in transient transfection assays of B-lymphoid cell lines, but did not impair the responsiveness of the BLV promoter to the virus-encoded transactivator Tax(BLV). Moreover, ectopically expressed PU.1 and Spi-B proteins transactivated the BLV promoter in a PUbox-dependent manner. Taken together, our results provide the first demonstration of regulation of the BLV promoter by two B-cell-specific Ets transcription factors, PU.1 and Spi-B. The PU.1/Spi-B binding site identified here could play an important role in BLV replication and B-lymphoid tropism.

Leptin activates the promoter of the interleukin-1 receptor antagonist through p42/44 mitogen-activated protein kinase and a composite nuclear factor kappa B/PU.1 binding site

We have recently shown that leptin strongly induces the expression and secretion of the interleukin-1 receptor antagonist (IL-1Ra) [Gabay, Dreyer, Pellegrinelli, Chicheportiche and Meier (2001) J. Clin. Endocrinol. Metab. 86, 783-791] in monocytes. However, the intracellular signalling mechanisms involved remained unknown. We now demonstrate that the activation of the IL-1Ra promoter by leptin is strictly dependent on the presence of the long form of the leptin receptor (OB-Rb), and that it also requires the activation of the p42/44 mitogen-activated protein kinases (MAPKs) as well as the presence of a nuclear factor kappaB (NF-kappa B)/PU.1 composite site at position -80 of the IL-1Ra promoter. Although leptin is capable of activating a NF-kappa B reporter element in transient transfection experiments, the protein complex binding to the NF-kappa B/PU.1 site of the IL-1Ra promoter is not composed of the p65/p50 subunits of NF-kappa B, as is evident in electrophoretic gel mobility-shift experiments. In contrast, a protein complex which does not contain PU.1 binds to this composite element in a leptin-dependent manner. In summary, we characterize the signalling pathway for leptin and OB-Rb involved in the induction of IL-1Ra, involving p42/44 MAPK, and a yet uncharacterized complex of transcription factor(s) binding to a NF-kappa B/PU.1 composite element of the IL-1Ra promoter.

Interleukin-3 stimulation of mcl-1 gene transcription involves activation of the PU.1 transcription factor through a p38 mitogen-activated protein kinase-dependent pathway

We have previously demonstrated that the antiapoptotic gene mcl-1 is activated by interleukin-3 (IL-3) in Ba/F3 pro-B cells through two promoter elements designated the CRE-2 and SIE motifs. While the CRE-2-binding complex contains the CREB protein and is activated by IL-3 through the phosphatidylinositol 3-kinase/Akt-dependent pathway, the identity and cytokine activation pathway of the SIE-binding complex remains unclear. In this report, we demonstrated that PU.1 is one component of the SIE-binding complex. A chromatin immunoprecipitation assay further confirmed that PU.1 binds to the mcl-1 promoter region containing the SIE motif in vivo. While IL-3 stimulation does not significantly alter the SIE-binding activity of PU.1, it markedly increases PU.1's transactivation activity. The latter effect coincides with the increased phosphorylation of PU.1 following IL-3 activation of a p38 mitogen-activated protein kinase (p38(MAPK))-dependent pathway. A serine-to-alanine substitution at position 142 significantly weakens PU.1's ability to be phosphorylated by the p38(MAPK) immunocomplex. Furthermore, this S142A mutant is impaired in the ability to be further stimulated by IL-3 to transactivate the mcl-1 reporter through the SIE motif. Taken together, our results demonstrate that IL-3 stimulation of mcl-1 gene transcription through the SIE motif involves phosphorylation of PU.1 at serine 142 by a p38(MAPK)-dependent pathway.

Toll-like receptor 2 and 4 (TLR2 and TLR4) agonists differentially regulate secretory interleukin-1 receptor antagonist gene expression in macrophages

Treatment of macrophages with lipopolysaccharide (LPS) from Gram-negative bacteria or peptidoglycan (PGN) from Gram-positive bacteria activates multiple intracellular signaling pathways and a large, diverse group of nuclear transcription factors. The signaling receptors for PGN and LPS are now known to be the Toll-like receptors 2 and 4 (TLR2 and -4, respectively). While a large body of literature indicates that the members of the TLR family activate nearly identical cytoplasmic signaling programs, several recent reports have suggested that the functional outcomes of signaling via TLR2 or TLR4 are not equivalent. In the current studies, we compared the responses of the secretory IL-1 receptor antagonist (sIL-1Ra) gene to both LPS and PGN. Both LPS and PGN induced IL-1Ra gene expression; however, the combination of both stimuli synergistically increased sIL-1Ra mRNA expression and promoter activity, suggesting that the signals induced by PGN and LPS are not equivalent. While both LPS and PGN utilized the PU.1-binding sites in the proximal sIL-1Ra promoter region to generate a full response, additional distinct promoter elements were utilized by LPS or PGN. Activation of p38 stress-activated protein kinase was required for LPS- or PGN-induced IL-1Ra gene expression, but the p38-responsive promoter elements localized to distinct regions of the sIL-1Ra gene. Additionally, while the LPS-induced, p38-dependent response was dependent upon PU.1 binding, the PGN-induced, p38 response was not. Collectively, these data indicated that while some of the intracellular signaling events by TLR2 and TLR4 agonists are similar, there are clearly distinct differences in the responses elicited by these two bacterial products.

Regulation of transcription of the intracellular interleukin-1 receptor antagonist gene by AP-1 in mouse carcinoma cells

Interleukin-1 receptor antagonist (IL-1Ra) is involved in many processes, including epidermal inflammation and hyperplasia after irritation or injury. However, the mechanism by which intracellular IL-1Ra (icIL-1Ra) expression is regulated in mouse keratinocytes has not been reported. We found that the CH72 mouse carcinoma cell line constitutively expresses the icIL-1Ra mRNA. To study the transcriptional factors responsible for the constitutive expression of icIL-1Ra, we functionally characterized 4.5 kb of the 5' flanking region of the human icIL-1Ra gene in these cells. We first demonstrated that icIL-1Ra expression in these cells was regulated at the level of transcription. Deletion analysis of the promoter showed that regulatory elements for constitutive expression were located -158 to -49 bp upstream of the transcription start site for icIL-1Ra. We investigated the cis- and trans-acting factors required for icIL-1Ra expression. An activating protein-1 (AP-1) site was identified as the positive regulatory element necessary for the constitutive expression of the icIL-1Ra promoter in CH72 cells. Moreover, electrophoretic mobility shift assay and cotransfection experiments showed that c-jun and c-fos proteins bound to the AP-1 site and functionally transactivated the icIL-1Ra promoter in mouse carcinoma CH72 cells.

PU.1 and Multiple IFN Regulatory Factor Proteins Synergize to Mediate Transcriptional Activation of the Human IL-1β Gene

Both lymphoid and myeloid cells express two related members of the IFN regulatory factor (IRF) family of transcription factors, specifically IRF-4 and IFN consensus binding protein (ICSBP or IRF-8). We previously reported that macrophages express IRF-4 and in combination with the ETS-like protein PU.1 can synergistically activate a human IL-1beta reporter gene. Here we report that this synergy is mediated by a composite PU.1/IRF element located within an upstream enhancer known to confer cytokine- and LPS-inducible expression. In macrophages, synergistic activation of IL-1beta reporter gene expression was preferentially mediated by IRF-4, whereas IRF-4 and ICSBP were equally capable of synergizing with PU.1 when coexpressed in fibroblasts. Furthermore, coexpression of IRF-1 and IRF-2 dramatically increased the capacity of both PU.1/IRF-4 and PU.1/ICSBP to induce IL-1beta reporter gene expression in fibroblasts. The additional synergy observed with IRF-1 and IRF-2 coexpression is mediated by a region of DNA distinct from either the IL-1beta enhancer or promoter. We also assessed the capacity of these transcription factors to activate endogenous IL-1beta gene when overexpressed in human embryonic kidney 293 cells. Although ectopic expression of PU.1 alone was sufficient to activate modest levels of IL-1beta transcripts, endogenous IL-1beta expression was markedly increased following coexpression of additional IRF proteins. Thus, maximal expression of both a human IL-1beta reporter gene and the endogenous IL-1beta gene was observed in cells that coexpressed PU.1, IRF-4 (or ICSBP), IRF1, and IRF2. Together, our observations suggest that these factors may function together as an enhanceosome.

Transcriptional regulation of intracellular IL-1 receptor antagonist gene by IL-1 alpha in primary mouse keratinocytes

The inflammatory cytokine IL-1alpha mediates inflammatory reactions in skin and up-regulates the expression of other proinflammatory genes. We previously found that IL-1alpha also increases steady state mRNA levels for intracellular IL-1 receptor antagonist (icIL-1Ra) in primary mouse keratinocytes; however, the mechanism for this was unknown. Here we show that increased expression in primary keratinocytes is due to increased rates of transcription. To study the transcriptional regulation of icIL-1Ra expression induced by IL-1alpha, we functionally characterized 4.5 kb of the 5'-flanking region of the human icIL-1Ra gene. Deletion analysis showed that regulatory elements were contained in the -598- and -288-bp region upstream of the transcription start site. Then we investigated cis- and trans-acting factors required for icIL-1Ra expression and found that a NF-IL-6 site and a NF-kappaB site in the icIL-1Ra promoter were responsible for IL-1alpha-induced icIL-1Ra expression. Moreover, gel shift assays and cotransfection experiments showed that CCAAT/enhancer-binding proteins alpha, beta, and p65 bind to the NF-IL-6 site and NF-kappaB site, respectively, and functionally trans-activate the icIL-1Ra promoter. Finally, mutational analysis confirmed that these elements were both essential for maximal transcription induced by IL-1alpha.

Ets target genes: past, present and future

Ets is a family of transcription factors present in species ranging from sponges to human. All family members contain an approximately 85 amino acid DNA binding domain, designated the Ets domain. Ets proteins bind to specific purine-rich DNA sequences with a core motif of GGAA/T, and transcriptionally regulate a number of viral and cellular genes. Thus, Ets proteins are an important family of transcription factors that control the expression of genes that are critical for several biological processes, including cellular proliferation, differentiation, development, transformation, and apoptosis. Here, we tabulate genes that are regulated by Ets factors and describe past, present and future strategies for the identification and validation of Ets target genes. Through definition of authentic target genes, we will begin to understand the mechanisms by which Ets factors control normal and abnormal cellular processes.

Critical flanking sequences of PU.1 binding sites in myeloid-specific promoters

The myeloid-specific transcription factor PU.1 is essential for expression of p47(phox), a component of the superoxide-forming phagocyte NADPH oxidase. The consensus PU.1 binding sequence (GAGGAA) is located on the non-coding strand from position -40 to -45 relative to the transcriptional start site of the p47phox promoter. A promoter construct extending to -46 was sufficient to drive tissue-specific expression of the luciferase reporter gene, but extension of the promoter from -46 to -48 resulted in a significant increase in reporter expression. Mutations of the nucleotides G at -46 and/or T at -47 reduced both reporter expression and PU.1 binding, whereas mutations at -48 had no effect. The PU.1 binding avidity of these sequences correlated closely with their capacity to dictate reporter gene transcription. In parallel studies on the functional PU.1 site in the promoter of CD18, mutations of nucleotides G and T at positions -76 and -77 (corresponding to -46 and -47, respectively, of the p47phox promoter) reduced PU.1 binding and nearly abolished the contribution of this element to promoter activity. We conclude that the immediate flanking nucleotides of the PU.1 consensus motif have significant effects on PU.1 binding avidity and activity and that this region is the dominant cis element regulating p47phox expression.